Twin Probes' Moon Crash Today: How to Watch Live

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Two NASA moon probes are slated to slam into the rim of a lunar
crater today (Dec. 17), and the space agency will give viewers a
behind-the-scenes look at the dramatic action.

The twin
Grail spacecraft, known as Ebb and Flow, will crash
intentionally near the moon's north pole at 5:28 p.m. EST (2228
GMT) today, bringing their gravity-mapping mission to a
spectacular close. The event will be broadcast on NASA TV and
streamed live on the agency's website, beginning at 5 p.m. EST
(2200 GMT).

The coverage should last about 35 minutes and will include
interviews with Grail team members. The impact site will be in
shadow at the time of the crash, so no video of Ebb and Flow's
violent demise is expected, NASA officials said.

The $496 million Grail mission launched in September 2011 and
arrived in lunar orbit about three months later. Ever since, Ebb
and Flow have been zipping around the moon in tandem, detecting
the tiny changes in the distance between them caused by lunar
mountains, craters and subsurface mass concentrations that affect
gravity.

Scientists have used these measurements to create the most
detailed gravity map ever constructed for a celestial body.
The new map reveals that the lunar crust is almost completely
pulverized, suggesting the moon — and the other rocky bodies in
the inner solar system — were battered by long-ago impacts far
more violently than previously thought.

Ebb and Flow are now almost out of fuel. They would have hit the
lunar surface eventually anyway, so the mission team wants to
bring them down in a controlled fashion. They're slated to hit a
crater rim at a latitude of 75.62 degrees north and a longitude
of 26.63 degrees east — far from any sites of historical
importance on the lunar surface.